X2 Interface in LTE

With the removal of the RNC from the access network architecture, inter-eNB handover is negotiated and managed directly between eNBs using the X2-C interface. In LTE implementations that need to support macro diversity, the X2-U interface will carry handover traffic PDUs (Protocol Data Units) between eNBs. X2-C (control plane) signalling is carried by the X2AP (X2 Application Protocol), which travels over an SCTP association established between neighboring eNBs.



X2AP performs duties similar to those performed by RNSAP (Radio Network Subsystem Application Protocol), which operates between neighboring RNCs over the Iur interface in UMTS R99 networks. X2-U (user plane) traffic is carried by the existing GTP-U (GPRS Tunnelling Protocol – User plane), as employed in UMTS R99 networks. The facilities provided by the X2-U interface are only expected to be required if macro-diversity handover is supported.  Both sub-types of the X2 interface travel over IP: SCTP/IP for the X2-C and UDP/IP for the X2-U.





X2 Interface Architecture : -



The X2 interface is designed to provide a logical signalling and traffic path between neighbouring eNBs.  The term ‘neighbouring’ in this sense refers to eNBs that generate adjacent cells between which UEs would be expected to request handovers. The X2 interface is the functional successor to the UMTS Iur interface, which interconnects neighbouring RNCs.



An eNB is only expected to support X2 interfaces to neighbouring sites with which there is a realistic possibility of handover events occurring; an individual eNB would not be required to support X2 interfaces to all eNBs in the network. Indeed, the X2 is an optional interface and all of its functions can be performed indirectly via the S1 and the MME/S-GW if direct connections are not supported.

LTE fundamentals

The fundamentals of the LTE Radio interface and get an overview of the evolution of 4G telecommunication. This 19 minutes video is presented by Ericsson expert Sven-Anders Sturesson.

The tutorial gives an overview of the fundamental technology of Long Term Evolution (LTE). You will learn the basics of the LTE radio interface, including multiple input, multiple outputs (MIMO), OFDM, uplink and downlink, SIMO, TDD, FDD, channel coding and GSA.

 

http://www.ericsson.com/ourportfolio/ericsson-academy/online-tutorials/lte_fundamentals_module/player.html



Source: Ericsson

How to calculate Peak Data Rate in LTE

The Peak Data rate of LTE is about 400Mbps?   It’s in a simple way to calculate date rate in LTE.

First: Assume That 20 MHz channel bandwidth, normal CP, 64QAM  and  4x4 MIMO technology are used.

Second: Calculate the number of resource elements (RE) in a subframe with 20 MHz channel bandwidth:

12 subcarriers x 7 OFDMA symbols x 100 resource blocks x 2 slots= 16800 REs per subframe. Each RE can carry a modulation symbol.

Third:  Assume 64 QAM modulation and no coding, one modulation symbol will carry 6 bits.

The total bits in a subframe (1ms) over 20 MHz channel is 16800 modulation symbols x 6 bits / modulation symbol = 100800 bits. So the data rate is 100800 bits / 1 ms = 100.8 Mbps.

Fourth:  with 4x4 MIMO, the Peak Data rate goes up to 100.8 Mbps x 4 = 403 Mbps.

Remote OMT and Remote OMT over IP

The features Remote OMT (Operation and Maintenance Terminal) and Remote OMT over IP are updated to support the new RBS 6000 DUG-20/RUS-01 configurations. In MCPA backwards compatible mode, having a BTS G11A or newer in a BSS 07B-G10B network, the configuration of an MCPA is made using OMT. Configuration in MCPA single mode (BTS G11B with BSS G10B or newer) is made from the BSC, refer to Section 5.7 on page 43.

All TRXs in a DUG are connected to one or several RUSs. It is the connections between RUSs and antennas that will decide which MCPAs to use for which antenna sectors (cells).

Each antenna sector is configured in the OMT with the default configuration of 3*20W (3*43.0 dBm) per MCPA. If desired it is possible to choose a different number of TRXs per MCPA, and it is possible to choose some configurations where the total MCPA mean power will end up on less than 60 W (47.8 dBm). Also the levels 40W (46.0 dBm) and 20W (43.0 dBm) are available.

The chosen number of TRXs and MCPA maximum mean power corresponds to different GSM RUS HW activation codes, although there is no licensing mechnism involved in the OMT based configuration.

Automatic FLP - Frequency Load Planning

Automatic FLP will enable operators to run Frequency Load Planning (FLP) networks, including Synchronized Radio Networks, with minimum effort and maximum performance. The feature performs daily downlink interference matrix measurements and creates synchronization clusters for synchronization status monitoring. FLP parameters are continuously supervised and automatically adjusted to network changes when needed due to for instance lost synchronization, addition of TRX HW, or changes in hopping frequency sets. The parameters that are put under direct BSC control by Automatic FLP activation are, HSN, FNOFFSET, MAIOs, TSC and FSOFFSET.

By using Automatic FLP an operator will get the following benefits:

·         Maximum capacity gain from FLP (best parameter configuration always used. Parameter settings can be kept continuously optimized)

·         Maximizes performance in all types of FLP networks (for example lower drop call rate, better speech quality)

·         Reduced O&M cost for FLP networks (Ease of use). Parameter settings will be optimized made without user intervention.

·         Necessary parameter changes in response to unplanned network changes can be very fast

·         Possibility to monitor synchronization status for each cell. Enables immediate FLP reconfiguration after loss of synchronization.

GSM - LTE Cell Reselection

 Broadcasts LTE system information in the GSM network to enable idle and packet transfer  mode cell reselection from GSM to LTE networks.

Each GSM cell broadcasts information about:

• Neighboring cells (WCDMA and LTE)

• Thresholds for IRAT

• Priority between GSM, WCDMA and LTE cells

The information is broadcasted in the GSM network via the system information message SI2quater.

The main purpose with priority based cell reselection is to allow reselection to LTE, but at the same time it also introduces cell reselection based on priority towards WCDMA. This is an alternative to the existing non priority based cell reselection to WCDMA. When cell reselection to LTE is used, cell reselection to WCDMA will be priority based as well. In MSs not supporting priority based cell reselection, the non-priority based cell reselection to WCDMA is used if the feature "GSM-UMTS Cell Reselection and Handover" is activated.

Commands and Printouts

• RLSRI: Radio Control Cell, System Information RAT Priority, Initiate - This new command is used to inform that priority based cell reselection shall be used.

• RLSRC: Radio Control Cell, System Information RAT Priority Data, Change - This new command have three formats, one each for GSM, WCDMA and LTE. The purpose with the commands are to configure different priorities between GSM, WCDMA and LTE in the cells.

• RLSRE: Radio Control Cell, System Information RAT Priority, End - This new command is used to inform that priority based cell reselection shall be deactivated.

• RLSRP: Radio Control Cell, System Information RAT Priority Data, Print This new command prints the state of the priority based cell reselection.

• RLSEI: Radio Control Cell, System Information E-UTRAN Restriction, Initiate - This new command is used to black list individual E-UTRAN (LTE) cells for cell reselection per LTE frequency in each GSM cell.

• RLSEC: Radio Control Cell, System Information E-UTRAN Restriction, Change - This new command is used to black list specific LTE cell groups for cell reselection per LTE frequency in each GSM cell.

Common Channel Configuration in LTE

Common Channel Configuration

Uplink resource blocks are required to be allocated for uplink control signaling (PUCCH). The number of RBs will be dependent on bandwidth and loading.

Downlink resources are also allocated for downlink control signaling on the PDCCH channel. This is specified as the number of OFDM symbols (Control Format Indicator).

PDCCH and PUCCH allocations will have an impact on peak data throughputs and system capacity. The PDCCH power boost feature makes it possible to adjust the power of the PDCCH to match the actual number of needed Control Channel Element (CCE) resources. Use cases include beam forming coverage extension, range extensions for small cells and general increase of the PDCCH capacity, which is useful for e.g. VoLTE applications. The maximum power increase is 6 dB.

The feature can be used in conjunction with the Enhanced PDCCH Link Adaptation feature which can provide significantly increased PDCCH capacity, as the RBS better determines the number of CCEs to utilize for UEs, independently from PDSCH.

The Enhanced PDCCH Link Adaptation feature introduces a dedicated link adaptation capability for PDCCH. This allows the eNB to control the number of CCEs to be used in PDCCH allocations to be optimized for a specific PDCCH BLER target, rather than using a fixed offset from the PDSCH link adaptation. It is expected that this will significantly increase the number of UEs that can be scheduled per TTI, as it relates to PDCCH usage. 

Cell Reference Symbol Power Configuration

The Adjustable Cell Reference Symbol (CRS) Power feature (FAJ 121 3049) was introduced in L14A. This feature enables flexible setting of the CRS power (Pa) and also enables flexible setting of the type-B resource element power (PDSCH).

The feature improved flexibility for tuning and optimization of downlink resource element power allocation and can lead to improved DL throughput, such as in high dense networks.

The feature controls two factors:

• CRS Power Boost setting (Pa) in the range +3dB to -3dB, previously this value had been fixed by system constant to +3dB.

• Type-B resource element boosting (Pb/Pa) in the range {5/4, 1, 3/4, 1/2}, previously this value had been fixed by a system constant to 1.

X2 Application Protocol (X2AP)

The X2AP protocol is used to handle the UE mobility within E-UTRAN and provides the following functions:

·         Mobility Management

·         Load Management

·         Reporting of General Error Situations

·         Resetting the X2

·         Setting up the X2

·         eNB Configuration Update

Protocol specification

3GPP TS 36.423 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP)

X2 layer 1

 The main functions of X2 interface layer 1 are as following:

·         Interface to physical medium;

·         Frame delineation;

·         Line clock extraction capability;

·         Layer 1 alarms extraction and generation;

·         Transmission quality control.

Protocol specification

3GPP TS 36.421 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1

S1 Signalling Transport

S1 signalling bearer provides the following functions:

·         Provision of reliable transfer of S1-AP message over S1-MME interface.

·         Provision of networking and routeing function

·         Provision of redundancy in the signalling network

·         Support for flow control and congestion control

L2 - Data link layer

Support of any suitable data link layer protocol, e.g. PPP, Ethernet

IP layer

·         The eNB and MME support IPv6 and/or IPv4

·         The IP layer of S1-MME only supports point-to-point transmission for delivering S1-AP message.

·         The eNB and MME support the Diffserv Code Point marking

Transport layer

SCTP is supported as the transport layer of S1-MME signalling bearer.

·         SCTP refers to the Stream Control Transmission Protocol developed by the Sigtran working group of the IETF for the purpose of transporting various signalling protocols over IP network.

·         There is only one SCTP association established between one MME and eNB pair.

·         The eNB establishes the SCTP association. The SCTP Destination Port number value assigned by IANA to be used for S1AP is 36412.

Protocol specification

3GPP TS 36.410 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 general aspects and principles               

3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1

3GPP TS 36.412 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 signalling transport

IETF RFC 2460: "Internet Protocol, Version 6 (IPv6) Specification"

IETF RFC 791 (September,1981): "Internet Protocol"

IETF RFC 2474 (December 1998): "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers"

S1 layer 1

the main functions of S1 interface layer 1 are as following:

·         Interface to physical medium;

·         Frame delineation;

·         Line clock extraction capability;

·         Layer 1 alarms extraction and generation;

·         Transmission quality control.

Protocol specification

3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1

RF Optimization Processes

Network Optimization process involves the following activities:

• FIRST SET THE CRITERION (GOAL) OF OPTIMIZATION PROCESS
• BASELINE & TARGET KPI’s.
• DELIVERABLES
• CONDUCTING A BASELINE PHYSICAL AUDIT
• REMOVING ALL SERVICE AFFECTING ALARMS
• IDENTIFYING POOR COVERAGE AREAS
• IDENTIFYING CAPACITY CONSTRAINTS & OVERUTILIZED CELLS
• VARIOUS KPIs with Root-Cause-Analysis of problems.
• Frequency Plan (BCCH & TCH)
• Neighbor plan
• CONDUCTING A GSM SYSTEM PARAMETERS AUDIT
• Deliverables of an Optimization activity:
• Baseline Drive test comparison with post implementation results.
• Statistical comparison of baseline & improved network.
• Parameter Audit report.
• Physical parameter inconsistencies.
• Frequency & neighbor plan inconsistencies
• Recommendations for
• Coverage
• Capacity
• Physical Optimization
• Location Area Optimization.

LTE Interview Question and Answer ( QA)

1. What is LTE?

2. What's the difference between 2G, 3G & LTE?

3. What's the benefit of LTE?

4. What's technology applied in LTE? (Both in UL and DL).

5. What is LTE Architecture?

6. What is the EUTRAN?

7. What is LTE Network Interface?

8. What is LTE Network Element?

9. What's the maximum Throughput we can achieve from LTE?

10. In the market, which type/category of UE is available now?

11. Do you have any experience in LTE dimensioning/planning and Drive-testing?

12. What is main frequency band for LTE?

13. In coverage planning, what are the most influence factors?

14. In 3G, RSCP and Ec/Io are used to determine in coverage planning. How's about in LTE? And why?

15. What are the range of SINR, RSRP, RSRQ, MCS and CQI values?

16. What is the typical cell range of LTE?

17. How do you understand RB and how does RB impact on Throughput?

18. What is the typical value of latency?

19. Do we still need Scraming code planning in LTE? If not, why?

20. Please explain me about eNodeB, MME and core network layout.

21. For capacity planning, do we still need Channel element (CE) dimensioning? If not, why?

22. Have you experience in Atoll and Momentun?

23. Have you experience in XCAL and Agilent NiXT?

24. Please explain me about QoS and Scheduling in LTE?

25. Pls. explain me about MIMO, SIMO and TxDiV configuration?

26. How's about those configuration and expected throughput?

27. What are the types of HO? If so, pls. explain me a bit of best cell HO and coverage HO?

28. What is ANR in LTE?

29. What is SON and how does work in LTE?

30. How does Timing advance(TA) works in LTE?

LTE Advanced Key Features

LTE refers to the advanced version of LTE that is being developed by 3GPP to meet or exceed the requirements of the International Telecommunication Union (ITU) for a true fourth generation radio-communication standard known as IMT-Advanced. 4G LTE, whose project name is LTE-Advanced, is being specified initially in Release 10 of the 3GPP standard, with a functional freeze targeted for March 2011.

Following is the Key Features for LTE Advanced:

§  Peak data rates: Downlink – 1 Gbps and  Uplink – 500 Mbps.

§  Spectrum efficiency: 3 times greater than LTE.

§  Peak spectrum efficiency: Downlink – 30 bps/Hz; Uplink – 15 bps/Hz.

§  Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used.

§  Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission.

§  Cell edge user throughput to be twice that of LTE.

§  Average user throughput to be 3 times that of LTE.

§  Mobility: Same as that in LTE

§  Carrier Aggregation

§  Higher order MIMO

§  Relay nodes and Heterogeneous networks

§  Enhanced Inter-Cell Interference Coordination

§  Coordinated Multipoint (CoMP) Transmission – Formalized in 3GPP Release 11

Liquid Radio

Liquid Radio

Liquid Radio - Making radio networks active, adaptive and aware

Liquid Radio architecture shares resources such as antenna information across a broad area of the network, as well as balances traffic evenly over different bandwidths. It allows radio coverage and capacity to flow to wherever users need it most. Liquid Radio also enables operators to seamlessly integrate 3GPP radio access with Wi-Fi to use unlicensed spectrum.  Liquid Radio improves network efficiency by boosting capacity, balancing loads, enhancing QoS, raising uplink capacity for smartphones, and identifying and avoiding smartphone signaling. It also adds small cell capacity and unifies heterogeneous networks, as well as implementing award-winning self-organizing network (SON) functions to simplify network operations. High energy efficiency is achieved by low power consumption, integration of Rf to the antenna, minimized Rf losses and by an adaptive and cognitive radio network that can proactively align the ‘active’ cells with user demand to save energy.

Nokia Siemens Networks has also announced its innovative Flexi Multiradio Antenna System as part of the Liquid Radio architecture. Nokia Siemens Networks Liquid Radio adapts the capacity and coverage of your networks to match fluctuations in user demand. It maximizes network performance and minimizes operating costs by automating operations. It includes built on Software Suites, Single RAN Active Antenna Systems, Baseband Pooling and Unified and SON-enabled Heterogeneous Networks.

Nokia Siemens Networks Liquid Radio Software Suites

>  Liquid Radio LTE Software Suite

>  Liquid Radio WCDMA Software Suite

>  Liquid Radio GSM Software Suite

Single RAN Active Antenna Systems

Baseband Pooling Unified and SON-enabled Heterogeneous Networks

Active Antenna system (AAS)

An active antenna is an antenna that contains active electronic components.remote radio head (RRH) or antenna-integrated radio designs place the Rf module next to the passive antenna to reduce cable losses

Active Antenna system is developed by Nokia Siemens Network (NSN) to reduce network cost and increase network efficiency. It’s a smart antenna and beam is driven by software.

Active Antenna does not need to be merely passive elements. With intelligent integration, active antenna technology transforms traditional antenna to contribute to base station efficiency. This enables operators to significantly increase the capacity and coverage targets set for their network.

Active Antennas are highly flexible and can meet the needs of many scenarios. They also support rising feature complexity including higher-order MIMO and receiver diversity, while retaining a simple and compact form factor.

§  Carrier-specific tilting

§  System-specific tilting

§  Multi-operator network sharing

§  Boosting performance with SON

§  Lower overall site costs

§  Improved network availability

§  Higher energy efficiency and RF performance

§  Reduced network evolution costs

The benefits to be gained include boosted capacity and coverage, higher energy efficiency, lower site rental fees, lower wind loading and reduced investments as new radio technologies come on line and additional spectrum bands become available. As a result,
active antenna systems enable operators to not only cut site costs substantially, but to also more cost effectively meet the dynamic demands of their mobile customers.

It is clear that active antenna systems will bring about a step-change in the evolution of radio networks. Leading the field is the Nokia Siemens Networks Flexi Multiradio Antenna System, which is a vital part of Liquid Net. This radical new architecture helps operators to cost-effectively address unpredictable demand by creating networks that adapt instantly to changing customer needs, using existing capital investments more efficiently and generating entirely new revenue opportunities. It does this by unleashing frozen network capacity into a reservoir of resources that can flow to fulfill demand, wherever and whenever broadband is used.

AAS BENEFITS

The benefits of active antenna architecture over RRH based site architecture are many. First, there is a potential to significantly reduce the site footprint. Second, the distribution of radio functions within the antenna results in built-in redundancy and improved thermal performance, which can result in higher system availability (lower failure rates). Third, distributed transceivers can support a host of advanced electronic beam-tilt features that can enable improvements in network capacity and coverage; hence, it has the potential to lower capital and operational costs. Each of these features shall now be described in the following sections.